Aerosols can be produced through a process of controlled condensation or vaporization-condensation. Generally such a process involves vaporizing an aerosol material and saturating a carrier gas with the generated vapor. The carrier gas and vapor is then cooled under laminar flow conditions. The controlled cooling initiates condensation of the vapor to yield an aerosol. To improve monodispersity and concentration of the aerosol, a common technique called heterogeneous condensation (HC) can be used. The HC technique involves the use of condensation nuclei or seed particles to assist in the formation of the aerosol particles to produce highly concentrated monodisperse aerosols from various liquid and solid aerosol materials.
Typically, a low volatility material (LVM) is selected for use as the aerosol material. The LVM is heated to produce a saturated vapor in the presence of a carrier gas and non-volatile condensation nuclei or seed particles (particle sizes of less than 0.1 μM) under low flow conditions. The condensation nuclei provide the surface needed to initiate particle formation and growth.
The mixture of vapor and condensation nuclei is thereafter cooled in a controlled manner under laminar flow conditions. The resulting supersaturation causes the vapor to uniformly condense onto the condensation nuclei, thereby yielding a monodisperse aerosol with particles having a narrow size distribution. The resulting particle sizes can be varied over a wide range of from about 0.5 μm to 5.0 μm by adjusting the ratio of vapor mass concentration to the number of condensation nuclei.
There are several aerosol generators commercially available on the market, which utilize HC to produce aerosols. Such aerosol generators are used for a variety of applications including observing the behavior of aerosols of specific particle sizes in a particular environment, effects of aerosols on electronic equipment, for example, and the toxicological effects of chemicals when inhaled. However, up to now, the use of such aerosol generators for highly toxic chemical agent testing has been very limited.
Aside from agent specific issues such as potential thermal breakdown and chemical reactivity, one of the principle factors limiting the use of HC aerosol generators is the relatively large quantity of agent needed for operation and the corresponding safety concerns for working personnel. Current aerosol generators commercially available in the market typically require a relatively large loading volume of the aerosol material, normally at least 100 ml, to produce a practical aerosol sample. Such aerosol generators generally include a saturator where the vapor of the aerosol material is produced to saturate the carrier gas passing therethrough. The saturator typically includes a boiler for holding the aerosol material and a heating element operatively associated with the boiler to heat the aerosol material to the state of vaporization. The carrier gas is then bubbled through the heated aerosol material, whereby the released vapor saturates the carrier gas.
The saturators are inherently inefficient, and therefore, require a sizable amount of aerosol material to produce an aerosol over a given period of time. Aerosol generators utilizing such saturators are especially impractical where the aerosol material is toxic and minimal handling is desired or where the aerosol material is expensive or in short supply. Such aerosol generators can pose undue safety hazards to the operators particularly where the aerosol material is highly toxic or dangerous to handle.
Accordingly, there is a need to develop an aerosol generator designed to produce highly concentrated monodisperse aerosols from an aerosol material with enhanced efficiency and reduced loading volumes of the aerosol material. There is a further need for an aerosol generator capable of producing highly concentrated monodisperse aerosols over an extended period of time from a relatively small volume of an aerosol material. There is a further need for a compact and lightweight aerosol generator for providing improved portability and convenient operation in a containment system such as, for example, a glove box.